I have an old 1969 Evinrude 40hp outboard. I have had the engine for three years and every year it has given me issues. I have had is serviced by two different mechanics and recently have attempted to fix it with the help of my machine designer father. Motor starts and runs. Sometimes it will slip out of gear as I throttle up from slower speeds to higher. All the sudden it will go from normal progression and then no longer be pushing the boat forward. I then lower the throttle and it kicks back in. Also it is leaking lower unit oil. We just replaced the seals on the lower unit. Any ideas or a point in the right direction would be much appreciated. Also it is a short shaft. I have been told that it is very tough to find short shafts these days in this horse power?